This invention relates to electric motors in general and, in particular, to a brushless, direct current (dc) motor wherein a rotor or armature is revolved by sequential or cyclic excitation of a set of stationary field windings from a dc power supply.
In a typical conventional brushless dc motor (shown in FIG. 1 of the drawings attached hereto), a plurality of switching transistors are cyclically rendered conductive for brief lengths of time to cause respective field windings to be energized cyclically by a dc power supply. A rotor or armature, as in the form of a permanent magnet, rotates in response to the cyclic excitation of the field windings.
A problem with this type of dc motor is the disposal of the electric energy produced by the field windings upon nonconduction of the associated switching transistors. A conventional solution to this problem has been to connect a capacitor in parallel with each field winding via a diode. The capacitors are intended to absorb the voltage surges generated by the field windings upon nonconduction of the switching transistors. It is objected, however, to the provision of just as many capacitors as the field windings as they make the electrical construction of the dc motor complex and expensive.
The dc motor of the type in question has had another problem in connection with the rapid electrical braking of the rotor. A shorting switch in the form of a relay contact pair has heretofore been connected in parallel with each field winding to that end. The mechanical switches are of course very susceptible to malfunctioning and so have impaired the reliability of the dc motor.